Characterization of intermixing at metal-semiconductor interfaces by angle-resolved Auger-electron emission: Cu/Si(111)-7×7

Si($L_2$,3VV) and Cu($M_2$,3VV) Auger intensities from the Cu/Si(111)-7×7 interface have been measured in a polar-angle-resolved fashion for various Cu thicknesses. A simple theory of polar-angle-resolved Auger emission has been developed and used to extract atom-number densities for both Si and Cu as a function of depth. It is found that significant Si outdiffusion is triggered at 300 K by Cu coverage in excess of 2 Å with characteristic diffusion lengths for Si of ∼35% of the overlayer thickness. Cu diffusion into the substrate, if it occurs at all, is limited to characteristic penetration depths of 1 to 2 Å for all coverages. The increased extent of Si outdiffusion above 2 Å is accompanied by substantial changes in Cu distribution throughout the interfacial region; at 2 Å, the Cu density increases sharply from interface boundary to surface whereas above 2 Å, the Cu density is constant throughout the interface.